Merge PostHog self-hosted into a single PostHog provider

Fold POSTHOG_SELF_HOSTED into POSTHOG: one provider now covers Cloud (OAuth + region-pinned API key) and self-hosted (API key + instance URL), since both already share the driver, name resolver, and PostHogConnectorSettings{BaseURL}. The API-key form picks a deployment (Cloud US/EU or self-hosted URL); the resolver requires exactly one of region/instanceUrl.

Drop the POSTHOG_SELF_HOSTED enum value, registration, migration, and logo mapping. Extract the deployment selector into a dedicated PostHogDeploymentField component. Point the driver tests at us.posthog.com instead of the legacy app.posthog.com host.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/connector/provider/builtin.go

@@ -46,7 +46,6 @@ func NewBuiltinRegistry() *Registry {
 		onePasswordRegistration(),
 		openaiRegistration(),
 		posthogRegistration(),
-		posthogSelfHostedRegistration(),
 		pagerdutyRegistration(),
 		resendRegistration(),
 		sentryRegistration(),